Thermoplastic resins or resin compositions such as an acrylonitrile butadiene styrene (ABS) resin and a polycarbonate resin/ABS resin, or reinforced thermoplastic resin compositions prepared by reinforcing such thermoplastic resin compositions with inorganic fillers have been widely used as material for the housings of mobile devices such as laptop personal computers, tablet personal computers, mobile phones including smart phones, digital cameras, digital video cameras, or the like. In general, as a method for producing such housings, an injection molding method in which the above thermoplastic resin compositions can be shaped freely to some extent has been employed.
In recent years, housings of mobile devices have been demanded: to be thinner; to be tough enough to withstand the impacts and loads while being placed inside a bag or such containers; and to be able to be made greaseless for cost reduction. (Here, the phrase “able to be made greaseless” means that a sufficient sliding property can be obtained without using a grease due to the self-lubricating property of the resin composition, whereby the cost and labor involved in supplementing the grease can be omitted.) For meeting these demands, the thermoplastic resin compositions used for the housings are required to have a high sliding property in the absence of a grease and a good moldability at the time of molding, as well as high rigidity and mechanical strength (such as impact strength) to be achieved after being molded into a product.
However, ABS resins or polycarbonate resin/ABS resin blends that are not reinforced with an inorganic filler are poor in rigidity to be obtained when molded, and therefore cannot meet the demand for thinner housings.
When carbon fibers are used as the inorganic filler, it may be possible to balance the stiffness and mass of the resulting molded article. However, the carbon fiber-reinforced thermoplastic resin composition has an electromagnetic wave shielding property, and therefore cannot be used for wireless LAN type mobile devices. Moreover, since carbon fibers are black, the carbon fiber-reinforced thermoplastic resin composition cannot meet the demand for providing products in wide range of colors.
In view of the above, the use of a glass fiber-reinforced thermoplastic resin composition as a thermoplastic resin composition for housings has been under consideration.
A glass fiber-reinforced thermoplastic resin composition exhibits high rigidity when formed into a molded article, and therefore can be used for producing thinner housings. However, a molded article produced from such a glass fiber-reinforced thermoplastic resin composition has insufficient sliding property and impact resistance.
As a thermoplastic resin composition that can be used for obtaining a molded article having an excellent sliding property, the following composition has been proposed.
(1) A thermoplastic resin composition containing: a graft copolymer obtained by emulsion polymerization of monomers in the presence of an aromatic polycarbonate resin and an ethylene-propylene-nonconjugated diene rubber-containing crosslinked latex; and a hard copolymer composed an aromatic vinyl monomer and vinyl cyanide-based monomer (Patent Document 1).
However, the thermoplastic resin composition of (1) above is poor in rigidity to be obtained when molded, and therefore cannot meet the demand for thinner housings. Further, the molded products obtained from such a resin composition have poor impact resistance and mechanical strength, and the sliding property of such molded articles is still insufficient.
As a thermoplastic resin composition that can be used for obtaining a molded article having an excellent mechanical strength, the following compositions have been proposed.
(2) A reinforced thermoplastic resin composition containing an aromatic polycarbonate resin, a graft copolymer, glass fibers surface-treated with a water-soluble polyurethane, a glycidyl ether unit-containing polymer, and a phosphoric acid ester-based flame retardant (Patent Document 2).
(3) A reinforced thermoplastic resin composition containing a polycarbonate resin, a rubber-containing polymer, carbon fibers bundled with an epoxy-based sizing agent (Patent Document 3).
However, the reinforced thermoplastic resin composition of (2) above is not intended to improve the sliding property of a molded article produced therefrom.
Further, the reinforced thermoplastic resin composition of (3) above has an electromagnetic wave shielding property, and therefore cannot be used for wireless LAN type mobile devices. Moreover, since carbon fibers are black, the carbon fiber-reinforced thermoplastic resin composition cannot meet the demand for providing products in wide range of colors. Furthermore, no particular attention is paid to the sliding property of a molded article produced from the resin composition.
As a thermoplastic resin composition that can be used for obtaining a molded article having excellent appearance and sliding property, the following composition has been proposed.
(4) A reinforced thermoplastic resin composition comprising: an aromatic polycarbonate resin; a thermoplastic resin such as a graft copolymer formed by grafting an aromatic vinyl compound and a vinyl cyanide compound to a diene rubber component or a copolymer comprising an aromatic vinyl compound and a vinyl cyanide compound; a reinforcing filler; an olefin-based wax; a sliding property-imparting material such as a fluororesin; and a polyester elastomer (Patent Document 4).
However, the sliding property of a molded article produced from the reinforced thermoplastic resin composition of (4) above is still insufficient.
In addition to the reinforced thermoplastic resin compositions of (1) to (4) above, many reinforced thermoplastic resin compositions to which an epoxy compound is added have been proposed for the purpose of improving the sliding property and mechanical strength of the molded article. However, heretofore, there has not been proposed a reinforced thermoplastic resin composition which has excellent moldability and can be used for producing a molded article with excellent balance of sliding property, rigidity, impact resistance, mechanical strength and appearance